The selective conversion of short chain alkanes namely ethane, propane and butane (a by-product of petroleum processing and present in natural/shale gas) to olefins ethylene, propylene, the butenes, and butadiene respectively are important processes owing to its high commercial value of end products. The entire capacity of C2-C4 olefins worldwide is produced by three commercial processes; they are i) thermal cracking (pyrolysis or steam cracking), ii) catalytic cracking and iii) catalytic dehydrogenation. These processes suffer many disadvantages like rapid deactivation, high endothermicity and thermodynamic limitations. Oxidative dehydrogenation (ODH) of light alkanes is a commercially attractive route to produce alkenes. The main advantage is the exothermic nature of the reaction which avoids the thermodynamic constraints of other non-oxidative routes by forming water as a byproduct. Compared with the conventional steam-cracking method of dehydrogenating alkanes to olefins and current catalytic dehydrogenation processes, ODH could reduce costs, lower greenhouse gas emissions, and save energy. ODH can be carried out with various oxidants like oxygen, air, carbon dioxide, etc.
The products obtained by dehydrogenation of ethane and butane are commercially more important. Ethene is one of the important building block chemical which ranks first in production among organic chemicals. Ethylene is a base material for the production for variety of chemicals like low, linear low and high dense polyethylenes (LDPE, LLDPE, HDPE respectively, Ethylene dichloride (EDC), Vinyl compounds like Vinyl chloride, poly vinyl chloride (PVC), Vinyl acetate (VAM), Styrene and many functionalized compounds. This starts well with butane dehydrogenation where the product distribution is wide when compared to propane and ethane. On the other hand the major products formed during butane dehydrogenation is 1-butene, 2-butene (including cis and trans), 1,3-butadiene, propylene, ethylene. Components of the C4 stream are mainly consumed in the production of synthetic rubber (butadiene), polyethylene co-monomer (1-butene), specialty chemicals, engineering plastics and solvents. The main products obtained from the C4-olefins are hexa methylene diamine, Acrylonitrile, butadiene, styrene, Polymers based on butadiene and butane.
In recent years, butenes, especially 1,3-butadiene became a versatile chemical as a monomer in polymer industry. Current industrial process for the production of butenes is the steam cracking of naphtha. As an alternative method, dehydrogenation of n-butane requires high temperature and it will favor more of cracked products and increases coke formation which will lead to quick catalyst deactivation. Meanwhile researchers have put on efforts in finding a robust catalyst for an energy efficient process like oxidative dehydrogenation (ODH). A large number of metal oxide systems are studied for ODH of n-butane. Few reports for ODH of ethane, propane, octane and ethyl benzene are available over titania supported systems. Cobalt based catalysts are well known for Fischer Tropsch reaction and other related synthesis.
US20030065235A1 discloses a method for converting alkanes to olefins comprising: heating a feed stream comprising an alkane and an oxidant to a temperature of approximately 300-700° C.; contacting said feed stream with a catalyst comprising a base metal, metal oxide, or a combination thereof and a refractory support; maintaining a contact time of said alkane with said catalyst for less than 200 milliseconds; and maintaining oxidative dehydrogenation favorable conditions; wherein ethylene yield is at least 40%.
U.S. Pat. No. 6,858,768B2 discloses a method for the production of olefins by oxidative dehydrogenation wherein the method comprises the steps of: (a) forming a feed stream comprising an alkane and an oxidant; (b) heating the feed steam to a temperature of approximately 300-700° C.; (c) contacting the feed stream with a catalyst consisting essentially of one or more oxides selected from the group containing alumina, zirconia, titania, yttria, silica, niobia, and vanadia; (d) maintaining a contact time of the feed stream with said catalyst for less than 200 milliseconds under oxidative dehydrogenation favorable conditions so as to produce olefins; and (e) recovering olefins; wherein the recovered olefins include ethylene and the ethylene yield is at least 50%.
EP0832056B1 discloses a process for converting an alkane of the formula, CnH2n+2, to an alkene of the formula, CnH2n, where n is the same for the alkane and the alkene and n is from 2 to 5, the process comprising contacting the alkane in the absence of oxygen with a dehydrogenation catalyst and a solid oxygen source comprising a reducible metal oxide under conditions sufficient to selectively convert the alkane and reducible metal oxide to a reduced form of the metal oxide, the alkene, and water, wherein the dehydrogenation catalyst comprises at least one metal selected from Cr, Mo, Ga, Zn, and a Group VIII metal, and wherein the reducible metal oxide is an oxide of at least one metal selected from Bi, In, Sb, Zn, Tl, Pb and Te.
WO2006063230A1 discloses a method of converting paraffinic hydrocarbons to alkenes, comprising the steps of: employing a perovskite composition, the composition having the general formula of BaSmTiO3, wherein in the composition, barium comprises from about 1 mole to about 2 moles, samarium comprises from about 0.1 mole to about 1.0 moles, and titanium comprises about 1 mole; heating a reactor which contains the composition to a temperature ranging from about 400° C. to about 500° C. using a gas and a means for heating; supplying a feed gas to the heated reactor, the feed gas comprising one or more paraffinic hydrocarbons, a quantity of oxygen, and a quantity of nitrogen, and wherein heat derived from converting the feed gas paraffinic hydrocarbon to alkenes heats the reactor to a temperature ranging from about 650° C. to about 1000° C., under conditions sufficient to convert the paraffinic hydrocarbon into one or more alkenes; and collecting the gasses exiting the reactor, wherein the alkenes are present in the collected gasses, the yield of C2+ compounds is greater than 20%.
U.S. Pat. No. 5,593,935 discloses a dehydrogenation of an alkane to an alkene, especially isobutane to isobutene carried out in admixture with oxygen and in the absence of added steam over a dehydrogenation and oxidation catalyst comprising a platinum group metal deposited upon a support, wherein the yield of desired alkene is in the range of 15 to 40%.
Article titled “Oxidative dehydrogenation of ethane over a perovskite-based monolithic reactor” by F Donsi e al. published in Journal of Catalysis, 2002, 209, pp 51-61 reports oxidative dehydrogenation (ODH) of ethane investigated in a short-contact-time reactor consisting of a LaMnO3-based monolithic catalyst with a honeycomb morphology. Using an ethane/air mixture with a C2H6/O2 ratio=1.5 and a preheat temperature ranging from 250 to 400° C. results in a 55% ethylene yield.
Article titled “Oxidative dehydrogenation of ethane over some titanates based perovskite oxides” by T Hayakawa et al. published in Catalysis Letters, 1992, 16 (4), pp 373-387 reports a series of perovskite catalysts tested for the oxidative dehydrogenation of ethane. The composition of these catalysts covered CaTi1-xFexL3-δ, with 0≤x≤0.4, SrTi1-xFexO3-δ, with 0≤x≤1.0, as well as mixtures of these. The maximum yield for ethene of 52% occurred at 1023 K with x=0.8.
Article titled “The oxidative dehydrogenation of ethane by perovskite type catalysts containing oxides of strontium, cerium and ytterbium” by OJ Velle et al. published in Catalysis Today, 1990, 6 (4), pp 567-574 reports the compounds with the general formula SrCe1-xYbxO3-0.5x characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), temperature programmed reduction (TPR) and BET, and its catalytic activity with respect to dehydrogenation of ethane to ethene. The different catalyst compositions were tested in a continuous flow tubular reactor with two different partial pressures of oxygen at 500, 600 and 700° C. A maximum yield of 49% was obtained at 700° C.
Article titled “Lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene working with redox mechanism” by R Watanabe et al. published in Front Chem.; 2013; 1; 21 reports lanthanoid-free perovskite oxide catalyst for dehydrogenation of ethylbenzene. The catalyst Ba0.4Sr0.6Fe0.6Mn0.4O3-δ showed high styrene yield of 29.2% and selectivity to styrene of 96.6% at 813 K.
Article titled “Novel Perovskite-Type Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene” by R Watanabe published in Catalysis Letters, 2009, 131 (1-2), pp 54-58 reports novel LaMnOx perovskite-oxide (ABO3) catalysts for effective catalytic dehydrogenation of ethylbenzene to produce styrene. Results show that the A-site in perovskite-type oxides affected catalytic dehydrogenation activities and that the B-site affected stability of the activities. The yield of styrene is in the range of 15 to 45%.
Article titled “Titania-Supported Cobalt and Cobalt-Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation” by Y Brik et al. published in Journal of Catalysis; 2001, 202 (1), pp 118-128 reports TiO2-supported Cobalt and cobalt-phosphorus catalysts prepared by impregnation and their performances in ethane oxidative dehydrogenation. The best performance in ethane ODH is achieved at 550° C. with the sample containing 7.6 wt % Co. The reaction begins with a conversion of 33% and selectivity around 75%, then it decreases to reach after 150 min on stream a stationary state at 22% of conversion and 60% selectivity.
The present invention provides an improved process for conversion of alkanes to alkenes which is economic, efficient and has high yields.